settings: Clear all PerAccountSettingsState on RESET_ACCOUNT_DATA

Really an instance of zulip#4446 that I forgot about in zulip#5606, oops.

Related: zulip#4446

Author: chrisbobbe

src/settings/__tests__/settingsReducer-test.js

@@ -10,12 +10,41 @@ import {
 import type { InitialData } from '../../api/initialDataTypes';
 import type { UserSettings } from '../../api/modelTypes';
 import { EventTypes } from '../../api/eventTypes';
-import settingsReducer from '../settingsReducer';
+import settingsReducer, { initialPerAccountSettingsState } from '../settingsReducer';
 import * as eg from '../../__tests__/lib/exampleData';
 
 describe('settingsReducer', () => {
   const baseState = eg.baseReduxState.settings;
 
+  describe('RESET_ACCOUNT_DATA', () => {
+    test('resets per-account state without touching global state', () => {
+      const prevState = [
+        // per-account
+        eg.mkActionRegisterComplete({
+          user_settings: {
+            /* $FlowIgnore[incompatible-cast] - testing modern servers, which
+               send user_settings. */
+            ...(eg.action.register_complete.data.user_settings: $NonMaybeType<
+              InitialData['user_settings'],
+            >),
+            enable_offline_push_notifications: false,
+            enable_online_push_notifications: false,
+            enable_stream_push_notifications: true,
+            display_emoji_reaction_users: true,
+          },
+        }),
+
+        // global
+        { type: SET_GLOBAL_SETTINGS, update: { theme: 'night' } },
+        { type: SET_GLOBAL_SETTINGS, update: { language: 'fr' } },
+      ].reduce(settingsReducer, eg.baseReduxState.settings);
+      expect(settingsReducer(prevState, eg.action.reset_account_data)).toEqual({
+        ...prevState,
+        ...initialPerAccountSettingsState,
+      });
+    });
+  });
+
   describe('REGISTER_COMPLETE', () => {
     test('changes value of all notification settings (legacy, without user_settings)', () => {
       const prevState = deepFreeze({

src/settings/settingsReducer.js

@@ -1,6 +1,8 @@
 /* @flow strict-local */
+import type { GlobalSettingsState, PerAccountSettingsState } from '../reduxTypes';
 import type { SettingsState, Action } from '../types';
 import {
+  RESET_ACCOUNT_DATA,
   SET_GLOBAL_SETTINGS,
   REGISTER_COMPLETE,
   EVENT_UPDATE_GLOBAL_NOTIFICATIONS_SETTINGS,
@@ -9,30 +11,33 @@ import {
 import { EventTypes } from '../api/eventTypes';
 import { ensureUnreachable } from '../types';
 
-const initialState: SettingsState = {
-  //
-  // GlobalSettingsState
-  //
-
+const initialGlobalSettingsState: $Exact<GlobalSettingsState> = {
   language: 'en',
   theme: 'default',
   browser: 'default',
   experimentalFeaturesEnabled: false,
   markMessagesReadOnScroll: 'always',
+};
 
-  //
-  // PerAccountSettingsState
-  //
-
+/** PRIVATE; exported only for tests. */
+export const initialPerAccountSettingsState: $Exact<PerAccountSettingsState> = {
   offlineNotification: true,
   onlineNotification: true,
   streamNotification: false,
   displayEmojiReactionUsers: false,
 };
 
+const initialState: SettingsState = {
+  ...initialGlobalSettingsState,
+  ...initialPerAccountSettingsState,
+};
+
 // eslint-disable-next-line default-param-last
 export default (state: SettingsState = initialState, action: Action): SettingsState => {
   switch (action.type) {
+    case RESET_ACCOUNT_DATA:
+      return { ...state, ...initialPerAccountSettingsState };
+
     case REGISTER_COMPLETE: {
       const { data } = action;